RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

Hey fellas, are there any other options besides the jag muffler? I gutted my stocker and it runs well, but it's still fairly heavy.

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

The Ryobi I'm working up now was my first gasser too and it's been flying a GP Giant Super Sportster since spring a year ago (see my avitar). I had done some mods on the motor before I put it in the GSS. It was then pulling about 11.5 lbs thrust on an APC 18x8W. Since then I've done some more work on the motor, the results of which are in this thread, and now I'm up to about 15 lbs thrust. I've yet to put it back in the plane but I think I'll be pleased with the result. The airframe all up ready to fly is 14.5 lbs, not a light weight for sure, but now with a 1:1 thrust to weight ratio it should be pretty good! No unlimited vertical but sporty I suppose!

diceco

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

Suprisingly Jtech Radiowave does not list one for the Ryobi but they claim they can make one.[link]http://www.jtecrc.com/incowlmufflersgas.htm[/link]

diceco

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

www.wackerengines.com has conversion parts for the Ryobi including a muffler.

Jim

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

If it is a Glo Bee tach you happen to be using, it is famous for giving strange readings. The only thing you can do is move the tach around while taking readings, and when you get one that is believeable, you are probably ok. I had one do this, and I even put a shroud around the photocell trying to make it work better. Didn't help. Too bad, because I rather like the tach other than the erroneous readings it gives. The only time it gives good steady readings however, is when it is pointed at a light. Then it gives the magic "3600" just fine...

AV8TOR

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

Thank you for the update. All I am looking for, is a fun sport flyer. sounds like the ryobi will do the job. I will tinker with it a bit to see what it will do.

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

Jack i dont think its so much what piston you use or what mods you have done to it. no matter what mods or what ring gap or how many ring ect ect if it wont seal its no good. Only way to know how your set up is is with a leakdown testor. I think i would even say that no matter what ring and piston combo you have if you test it with a leakdown testor with a .023 orfice and get a 100 over 100 reading with a 13 second time from valve close to 0 psi leakdown count then your gona get a stock motor with a larger 12.7 or 11.1mm venturi carb close to or around 7500 rpm.

It seems these are the most important factors.
#1 a cylinder ring combo with as little leakage as possible and
#2 a larger carb

eveything else just dosent seem to work I know others have had some gains in increasing the port timming and that just hasent been the case for me and i had done that mod twice with two different cylinders. the gains others got from this mod i think are on cylinders that are very different from mine. i know for sure your using the two runner per side and getting results close to mine with this mod so yes it probably works on that type cyl. on mine nope no cigar lol.


I started out today to do the rest of my testing. I had my engine all ready to go with the port mods and test ran recorded 7530 rpm with a static thrust of 14 lbs 2 oz. so absolutly no change there.

Next i converted to the electronic ignition. when test ran it seem to lose rpm and performance. this puzzles me greatly. I had the timming set to 28 degrees advanced as I understand how to set the timming. i degreed in 28 degree advance and set the sensor in the middle of the magnet. when test run i was getting 7280 rpm and 13 lbs 2 oz thrust.

I was able to gain back some of the power by hand tunning the timming and testing retime and test and retime and kind of adjust for performance. best i could get was 7440 rpm @ 13 lbs 13 oz thrust.

Even though the electronic ignition seemed to lose power it was so easy to start. just a light flip and man it was off and running. this thing also has a great advance curve so at idle the timming is retarded to where the idle is so smooth. yo can idle so low you can darn near count the prop blades go by. SERIOUSLY the idle and starting was drastically improved and this was worth it right there.

From here im pretty much done testing this engine. It is more than adequate for the plane im gona put it on and its getting nice out so its time to go fly.

I am gona start another conversion that can be tested on further.

With the set up I currently have there is something limmiting this engine to or around the 7500 rpm range. no matter what I do other than the making sure I have a good cylinder to ring seal and providing all the compression i can get and a larger carb nothing else works in any tangible gain in power. I dont know if there is something holding back this set up or if it has just plainly reached a point to where there is no more to get out of this engine with this CC range. it seems the only way to get more power from here is more CC.

I did check the port volume on the two runner cylinder and it has a volume with the two runners together of 2 ml. so that would be a 4 ml port volume altogether. sorry got no way to convert this to cc.
The cylinder witht the one runner port has a capacity of 2.6 ml so that would be a total port volume of 5.2 ml. interesting that my cylinder has the larger ports but yet it dosent repond to the port timming modification.

I dont know what else i can try. I do however think that if i take a stock ryobi and get it to have around a 13 second leakdown count at 100 over 100 reading and put a 12.7 mm venturi carb on it it should run around 7500 rpm. I guess this will be where i will start when I do my next test engine. I will know that alll the mods discussed here so far will do nothing to improve this number and from there i need to go new directions.

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

When you time an ignition set up you DO NOT TIME the location of the sensor and magnet, there are too many variables in the sensitivity of the sensor and the strength and width of the magnet.
You set up your degree wheel correctly and turn on the ignition and rotate the prop hub in the direction of normal rotation, when it sparks that's the timing. Adjust until it sparks @ 28-30 degrees BTDC.

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

Terry is right. (of course) ;)

Plus, since you have it running, you could make a mark where your sensor is now. Then advance it a small amount, test run it, etc. Once it quits improving in rpms, go back to your last setting before that and call it "good'.

BTW, 7500 on an 18 x 8 prop isn't bad for a Ryobi....

AV8TOR

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

yea thats pretty much what i did.

I know 7500 is pretty darn good and i think the dynathrust prop take a bit of power to swing it. im not complaining i just find it interesting that all the stuff ya hear to make these run better most of it just dosent work. you know what my opinion is now lol.

Damn thats good to know. I dont know where i got the info to set it up in the middle of the magnet. I guess that makes sense to do it thais way. The only thing i dont understand is wont the spark be retarded for the low rpm or will it fire at full advance and if it fires at full advance when does it retard the spark? if you set it up this way then when its at full throttle will your total advance be 28-30 deg btdc? this 28-30 btdc is what the stock magneto runs at as i have confirmed this with a timming light and timming marks i drew on the engine shaft hub and flywheel when i degreed it in. I did notice when rotating it through that the spark was after the magnet was leaving the sensor so i knew the setting it in the middle of the magnet was bull at that point.

I got to say i was very dissipointed in no power gain going to electronic. I was sure losing the flywheel weight and drag and the drag of the magnet on the coil woild gain some power but no cigar on that one. well i guess if i get it timmed properly that may change. one thing for sure I do love the hand proping of it and how stinking easy it starts and idles.

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

Hey combat, about the ml to cc, 1ml=1cc. no conversion necessary. Im glad that your happy with the final results. I intend on getting my ryobi fixed (i just so happen to have the right tap to fix the threads) and hope to run it soon. I will be using a 18-8 top flite prop. I also have to wait for warmer temps in order for my tach to work.

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

The computer timing chip is smarter than any 3 modelers combined:D Over 200 RPM it is full retard, ie 25 degrees of timing change. The average hand flip is 500-600 rpm. So a 30 deg BTDC static timing becomes 5 deg BTDC when starting, thats why it doesn't kick.

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

Well that makes a lot of sense. I still dont understand how the very first pop is gona bee retarded as its takes at least two times through the sensor to get a speed. mine you can put it just before the sensor and flip it through and it will pop off and run. I guess its probably not retarded at that point till it hits the second time through the sensor.

so if your just pulling it through slowly by hand to see where it sparks then it sparks at full advance right?

Well that sure makes for a simple conversion lol.

I am going to denver for a week to get a mill and a lathe but when i get back i plan on putting together another leakdown testor. I will put it together with a dynathrust test prop and i will send it to someone on here. from there he will pass it on to the next guy and it can just go around so we all get a chance to test off of the same test standards. I think i will also start a journal to send with it. in it i will list all my mods and test readings and the next guy can list his. when it comes back my way we can post all the results. that should be very interesting huh. kind of a standardized test kit. maybee i can even put the laser digital tach in it to. then we would have a standard tach and no guessing on tach differences. I could even put in it my timming tools and degree wheel so we all can get good timming info. i can put it all together in a tool case so it would be easy to ship.

dang i like this idea.

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

Been away for a spell. Glad to see there's still interest in the Ryobi engine. Still have my Got Gas R/C Sport and Trainer on Ryobi 31s. www.gotgasradiocontrol.com Gotta go back and start reading this thread from Post 1. Looks like a lot of reading. [sm=spinnyeyes.gif]

R.C.

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

I'm not sure what your port volume measurement is. How did you measure it and what does port volume mean to the performance of our motors?

diceco

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

Naw its smarter than that. It can tell the RPM on the first turn. It measures the dwell time of the magnet under the sensor and compaires it to 4mhz clock. So the size of the magnet is important. Its calabrated to work with andyhing smaller than 1/4" inch dia.

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

ok heres what I did. I took a clear piece of packing tape. I placed it on the inside of the cylinder wall so it covers the port and follows the contour of the cylinder wall. I then used a graduated syringe to fill the port with water till it reached the top just even with the base of the cylinder.

As far as what port volume does thats what i would like to know. it would seem that if it had a larger port volume then it would flow more air. this may not be the case though as it will flow in a larger port in a slower velocity. larger not always better.


again on the ignition so if your pulling it through by hand to set the timming then it will fire at full advance right? that would be the point of setting it to where it fires at 28-30 deg btdc right?

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

RIGHT

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

Gordon Jennings in his book under the heading "Port Timing" gives a thorough analysis on how the two stroke engine porting systems work. He argues astutely that the flow of the port is a function of it's mean cross sectional area (the mean area of the port as the piston opens and closes the port during the cycle, not the total port area) and the amount of time the port is open in crank degrees.

He has developed a parameter he calls "time-area", an idea that was actually first introduced by Yamaha engineers. He then normalizes this time-area parameter (divides) by the swept volume of the piston in the cylinder (displacement). This simply means that for a bigger cylinder you need bigger ports! He has found that with this calculation you can then introduce engine speed into the calculation and tune the ports to work at what ever speed you desire to obtain peak torque.

So, although port volume may take a part in the performance of the two stroke motor, affecting things such as port scavenging because of the different velocities as you mentioned, it is probably of only secondary effect. The first order effect is the cross sectional area of the port and the duration of it's opening.

Do read Jennings section on Port Timing, for he does a much more thorough job of describing the concept than I.

diceco

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

That somewhat makes sense. If you take a dial caliper and measure the my port width it is .400. If you measure the ports on the two runner cylinder it measures .300 per port.

that means the total port area exposed when the port is exposed is greater on the two runner cylinder by .200 per side. and this is the cylinder that responds to the timming mod to.

the difference in volume is that the single runner ports are way deeper.

sounds like im gone have to do some port experimentation when i get my next ryobi converted and ready for testing. for right now im gona get this one on my plane lol

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

I have been reading Jennings' book also and lurking on this thread as well. I am pretty much a newbie to conversions but I do have a Ryobi that I converted and am still getting used to it. Right now it is down due to a crapped out ignition.

But from what I have been able to understand from Jennings, port timing and compression are not as important as port scavenging. In other words, how quickly we can get the exhaust out and the fresh new charge in. This is mostly controlled by the area of the exhaust ports and transfer ports and also by the direction and smoothness of the transfer ports. I am sure everyone has heard the term Schnerle porting on our glow engines. This is a reference to a man who came up with one of the best ways to arrange the transfer ports of a 2 stroke engine to bring the charge into the cylinder in an upward direction that then pushes the exhaust out. That is why the transfer ports are set at 90 degrees to the exhaust port, to keep the fresh charge from going straight across the piston and back out the exhaust port.

And from what I have been able to understand and how this would be applied to the Ryobi is:

First, there is not much gain to be had by changing the intake any as a reed type induction is pretty well regulated by the engine anyway. However the larger carb is needed to supply as much as it can take.

Second, getting a good seal on the piston is important to seal the exhaust out of the crankcase as exhaust into the crankcase dilutes the fresh fuel charge. Not to raise the compression. So a Bowman ring is a good thing to have.

Third, in order to get the exhaust out and the fresh charge of fuel in (which is the definition of scavenging), the exhaust restriction caused by the stock muffler must be changed. He goes into a long description of resonances and tuned pipes on the exhaust and how they help to draw the exhaust out and then stop the fresh charge from coming out but for our purposes, just opening up the muffler or using a conversion muffler is about the best we can do here.

Fourth, the transfer ports are good as is but if more scavenging is needed for more power, the best machining mod that can be done on this engine is to increase the area of the exhaust port. Not the timing.

Lastly, for the last optimization, the spark can be dialed in more closely using an electronic ignition.

From what I have inferred from all my reading on this forum and from Jennings book, the best steps we can do to convert a Ryobi are.

1. New ring from Bowman that will create a better seal in the cylinder.

2. Get a 10 to 11mm carb to match what the engine can draw from the intake reed.

3. Gut the muffler and make at least a 1/2"outlet for it or switch to a custom made conversion muffler.

4. Switch to electronic ignition so that the spark can be dialed in optimally. Not to mention making it easier to start.

At this point the engine will be close to the best it is going to get. But however, if one has the knowledge and the skills to go further to hop up the engine, the exhaust port area would be the best place to start. Jennings book can be used to make calculations on what the best areas would be best for the rpm desired.

So, this is what I think I have learned and gleaned from all my reading. Do all the assumptions sound correct? Or is my understanding off?


Jim

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

Sounds pretty good, though I use two outlets of around 7/16" i.d. on the muffler.

AV8TOR

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

You are right, I meant to say two. That is what I did on my Poulan 25cc motor. On my Ryobi, I cut a big rectangular hole out of the top of the stock muffler. After gutting it of course.

Jim

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

HEY COMBAT? If you are running "70" to Denver, I would buy your lunch or whatever at EXIT 17. My cell phone is 785 821 4381. After one more trip to the Wound Center in Garden City tommorow, 4-6, I plan on being around. Flathead

RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
 

Thats a pretty good summary JIMARRINGTON. See my .02$ below.

Perhaps it is a benifit in both regards, blow-by and compression. The stock single ring has such a huge end gap that I'll bet compression is suffering, and compression is torque as they say. The later model Ryobi's with the two ring piston has perfectly fine sealing rings as is. No need for a Bowman or any other ring on those.

Increased exhaust area can be gotten by increasing the width of the port, the height of the port, or both. It happens that if you increase the height of the port you also increase the duration (timing). This provides not only a larger cross section area of the port but it's also open for a longer time. This gives a greater value in the "time-area" calculation, from both area and timing, and gives even more exhaust flow than would if you just increased the projected area by increasing the width alone. I don't really agree that the timing should not be changed.

av8tor is using a 11.1mm venturi carb, combatpilot and diceco are using a 12.7mm carb. I'm not sure what others are using. I may have missed something but I have not seen any performance results for a Ryobi with a 10mm carb.

From the recent work that combatpilot has done an electronic ignition will not give any better top end performance. 28-30 degrees advance is pretty much standard for these motor it seems. combatpilot has measured this with the stock ignition. This means that there isn't much if anything to be gained by the ability to "dial it in". The electronic ignition sure does make it start and idle nice and it's a bit lighter but it's pretty pricey. Your $50 Ryobi project just doubled in price at a minimum.


diceco